Completely natural electroweak symmetry breaking is easily achieved in supersymmetric models if there is a SM-like Higgs boson, h, with m h < ∼ 100 GeV. In the minimal supersymmetric model, such an h decays mainly to bb and is ruled out by LEP constraints. However, if the MSSM Higgs sector is expanded so that h decays mainly to still lighter Higgs bosons, e.g. h → aa, with Br(h → aa) > 0.7, and if ma < 2m b , then the LEP constraints are satisfied. In this letter, we show that in the next-tominimal supersymmetric model the above h and a properties (for the lightest CP-even and CP-odd Higgs bosons, respectively) imply a lower bound on Br(Υ → γa) that dedicated runs at present (and future) B factories can explore.Low energy supersymmetry remains one of the most attractive solutions to the naturalness / hierarchy problem of the Standard Model (SM). However, the minimal supersymmetric model (MSSM), containing exactly two Higgs doublets, suffers from the "µ problem" and requires rather special parameter choices in order that the light Higgs mass is above LEP limits without electroweak symmetry breaking being "fine-tuned", i.e. highly sensitive to supersymmetry-breaking parameters chosen at the grand-unification scale. Both problems are easily solved by adding Higgs (super) fields to the MSSM. For generic SUSY parameters well-below the TeV scale, finetuning is absent [1] and a SM-like h is predicted with m h < ∼ 100 GeV. Such an h can avoid LEP limits on the tightly constrained e + e − → Z +b ′ s channel if Br(h → bb) is small by virtue of large Br(h → aa), where a is a new light (typically CP-odd) Higgs boson, and m a < 2m b so that a → bb is forbidden [2]. The perfect place to search for such an a is in Upsilon decays, Υ → γa. The simplest MSSM extension, the next-to-minimal supersymmetric model (NMSSM), naturally predicts that the lightest h and a, h 1 and a 1 , have all the right features [1,2,3,4,5]. In this letter, we show that large Br(h 1 → a 1 a 1 ) implies, at fixed m a1 , a lower bound on Br(Υ → γa 1 ) (from now on, Υ is the 1S resonance unless otherwise stated) that is typically within reach of present and future B factories.In the NMSSM, a light a 1 with substantial Br(h 1 → a 1 a 1 ) is a very natural possibility for m Z -scale soft parameters developed by renormalization group running starting from U (1) R symmetric GUT-scale soft parameters [5]. (See also [6,7] for discussions of the light a 1 scenario.) The fine-tuning-preferred m h1 ∼ 100 GeV (for tan β > ∼ f ew) gives perfect consistency with precision electroweak data and the reduced Br(h 1 → bb) ∼ 0.09 − 0.15 explains the ∼ 2.3σ excess at LEP in the Zbb channel at M bb ∼ 100 GeV. The motivation for this scenario is thus very strong.Hadron collider probes of the NMSSM Higgs sector are problematical. The h 1 → a 1 a 1 → 4τ (2m τ < m a1 < 2m b ) or 4 jets (m a1 < 2m τ ) signal is a very difficult one at the Tevatron and very possibly at the LHC [8,9,10,11]. Higgs discovery or, at the very least, certification of a marginal LHC Higgs signal will requi...