There is a high demand for the development of new carriers for pharmaceutical forms for human, veterinary, and animal-feeding use. One of the solutions might be bioactive compound-loading pellets for animal forage. The aim of the work was to assess the physical and sensory properties of forage with the addition of onion peel and off-spec onions as a source of quercetin. The feed was prepared using an expanding process (thermal–mechanical expanding process). Quercetin content was evaluated in raw onion and in final-product feed mixture samples (before and after expanding, and pelleting). The obtained feed was subjected to sensory analysis, testing for expanded pellet uniformity, water absorption index (WAI), the angle of a slide, and antioxidant activity. The results confirmed a high recovery of the quercetin after the expanding process (approximately 80%), and a significantly reduced intensity of onion odor, which was confirmed compared to the non-expanded onion, which is beneficial. Furthermore, digital and optical microscopy were applied for structure analysis. Microscopic imaging results confirmed that the onion structures were visible in the whole length of feed material and analyzed cross-sections. The results can be an introduction to further research on developing products that use the expanding and pelleting process to exploit the peel and off-spec onions, as well as other waste raw materials.