Combine lime juice, chicken broth, cilantro, garlic, and cornstarch. Set aside.
Sprinkle beef with cumin, salt, and black pepper; toss to coat. Coat an unheated large skillet with cooking spray. Add onions and sweet peppers. Stir-fry over medium heat for 3 to 4 minutes or until crisp-tender. Remove vegetables from skillet.
Carefully add cooking oil to the skillet. Add beef strips; stir-fry about 3 minutes or until desired doneness. Push to side of the skillet.
Stir lime juice mixture; add to skillet. Cook and stir until thickened and bubbly; cook and stir 1 minute more. Stir meat and vegetables into mixture in skillet; heat through.
To serve, arrange greens and tomatoes on four dinner plates. Divide beef-vegetable mixture among plates. Top with Baked Tortilla Strips and serve with red or green salsa, if desired. Makes 4 main-dish servings.
Baked Tortilla Chips
Cut tortillas into 1/8- to 1/4-inch-wide strips. Place strips on a baking sheet. Coat with nonstick cooking spray. Combine paprika and chili powder; sprinkle over tortilla strips. Bake in a 400 degree F oven 5 minutes. Toss; bake 3 to 5 minutes more.