Edible insects are a sustainable food source to help feed the growing population. Mealworms (Tenebrio molitor) can survive on a variety of food wastes and alter their composition based on the feed source. Commercial carrot production produces an abundance of carotenoid-rich carrot pomace, which may be beneficial for mealworm larvae growth. This study uses an I-optimal response surface design to assess the effect of dehydrated carrot pomace concentrations (made up with wheat bran as the control) in the substrate and wet carrot pomace as the moisture source (potato and carrot as control moisture sources) in a mealworm-larvae-growing system. Using this design, statistical models were fit to determine the relationship between the substrate and moisture and dependent variables, which include mealworm larvae mortality, days to maturity, weight, protein content, fat content, moisture content, ash content, and total carotenoid content. An optimum diet was proposed, in which the best diet for improving commercial mealworm growth was found to contain 36% dehydrated carrot pomace in the substrate, with wet carrot pomace as the moisture source. This research provides an application for a commercial waste stream and provides insight to help improve the growth of a sustainable protein source.