Melt butter in a large skillet over medium-high heat; add mushrooms and bell pepper, and sauté 8 minutes or until tender. Remove from heat; cool slightly.
Whisk together eggs and next 3 ingredients in a large bowl until smooth. Stir in mushroom mixture, cottage cheese, and remaining ingredients. Pour into a greased 13- x 9-inch baking dish.
Bake at 400° for 15 minutes. Reduce heat to 350°; bake 15 more minutes or until set and lightly browned.