Preheat the oven to 350°F (175°C). Prepare a baking dish with nonstick spray.

In a saucepan, boil 2 cups of water. Add brown rice and a pinch of salt; cover and simmer for about 45 minutes until tender.

In a skillet, heat oil over medium heat. Sauté onions and garlic until fragrant (about 3 minutes), then add mixed vegetables and cook until vibrant but crisp.

In a large bowl, mix the cooked brown rice, sautéed veggies, milk, half of the cheddar cheese, salt, and pepper until well combined.

Transfer to the baking dish. Top with remaining cheese and breadcrumbs.

Bake for 25-30 minutes until bubbly and golden brown. Let cool slightly before serving.