Gluten-free breads enriched with maitake (Grifola frondosa) were developed to enhance functional value and evaluated for technological quality, antioxidant capacity, colour, texture, mineral composition, molecular features (FTIR), and consumer acceptance. Formulations containing 0–20% maitake (flour basis) were baked under standardized conditions. Compared with the control, the addition of maitake resulted in higher bread yield and moisture content, accompanied by a gradual reduction in specific volume as the level of supplementation increased. The enrichment also led to a significant improvement in nutritional quality, including higher protein and fat contents as well as enhanced levels of bioactive compounds (total phenolic content, total flavonoid content) and antioxidant capacity. Colour measurements indicated darker crumb colour with increasing levels of maitake, reflected by lower L* values, higher a* values, and largely unchanged b* and C* parameters. All enriched breads exhibited colour differences exceeding the perceptibility threshold (ΔE > 5). Texture analysis showed unchanged hardness up to 15% addition, with a significant increase at the highest level, while springiness decreased from 15%; cohesiveness and chewiness remained unaffected. Elemental analysis revealed increased mineral content, particularly potassium and zinc, which rose significantly from 5% addition and exceeded threefold levels at the highest supplementation. Spectroscopic analysis confirmed structural modifications within the bread matrix associated with interactions between mushroom components and the starch–protein network. Sensory evaluation revealed that breads containing low to moderate amounts of maitake were well accepted by consumers, whereas higher levels negatively affected flavour and texture. Overall, the results demonstrate that Grifola frondosa can be effectively used as a functional ingredient in gluten-free bread, enhancing its nutritional and antioxidant properties while maintaining acceptable technological and sensory quality, particularly at inclusion levels up to 5–10%.