Preheat oven to 350°. In a large skillet, cook beef with onion powder, 1/2 teaspoon salt, garlic powder, sage and pepper flakes over medium heat 6-8 minutes or until no longer pink; crumble beef; drain. Stir in spinach. Remove from heat.
Spread potatoes in a greased 13x9-in. baking dish; top with beef mixture. In a large bowl, whisk eggs, ricotta cheese, milk, pepper and remaining salt; pour over top. Sprinkle with cheese. Top with tomatoes.
Bake, uncovered, 45-50 minutes or until a knife inserted in the center comes out clean. Let stand 5-10 minutes before serving.