Whisk eggs with the seasonings; add meat, tomatoes and green chilies, and mushrooms; stir to combine.
Slow-cooker method: Pour ¾ bag frozen potatoes into greased slow cooker; top with 1½ cups cheese, then ¾ egg mixture. Layer rest of potatoes, then eggs on top; save remaining cheese for later. Cook on high 3-4 hours or low 6-8. Top with remaining cheese at the end.
Oven method: Put all of the potatoes in a greased 9×13 pan; pour mixture on top, bake at 350° for 45-55 minutes. Sprinkle with 2 cups shredded Cheddar cheese the last 5 minutes.