Prep the Ingredients: In a large bowl, combine the chopped mushrooms, onions, oats, salt, and pepper. Stir until everything is well mixed.
Add the Cheese: Stir in the shredded cheese (if using). This adds richness and flavor, but feel free to skip it if you're making these dairy-free.
Mix in the Eggs: Add the lightly beaten eggs to the mixture and stir well until all the ingredients are fully combined.
Season to Taste: Add any optional seasonings, like oregano or garlic powder, for an extra flavor boost. Customize to your taste!
Shape and Bake: To make muffins, spoon the mixture into muffin tins or shape the mixture into 4-6 patties for mushroom burgers or poppers. You can also press it into an 8x8 casserole or loaf pan sprayed with non-stick spray.
Bake and Enjoy: Bake in a preheated 350°F oven for 40-50 minutes, or until the muffins (or patties) are golden brown and firm to the touch. They should bounce back when pressed.