Preheat the broiler: Set the broiler to low heat.
Prepare lime crema: In a small mixing bowl, combine sour cream with lime zest. Stir until smooth and set aside.
Broil bell peppers: Place diced green bell peppers on a foil-lined baking sheet. Spray with olive or avocado oil and season with salt and pepper. Broil for 4-5 minutes, or until softened. Let the broiled peppers cool slightly before adding them to the vegetable mixture.
Prepare vegetable mixture: In a medium mixing bowl, combine the cooled broiled bell peppers, diced tomatoes, chopped cilantro, sliced radishes, red cabbage, remaining lime juice, minced garlic, and 2 tablespoon olive or avocado oil. Stir well and season with salt and pepper. Taste the mixture and adjust seasoning if necessary.
Cook carne asada: Heat a non-stick pan over medium-high heat. Add 2 tablespoon olive or avocado oil. If your carne asada strips are very thin, cook for 1-2 minutes per side until browned and fully cooked through. For thicker pieces, cook slightly longer until fully cooked through. Transfer the meat to a cutting board and chop into ⅛-inch pieces.
Crisp tortillas: Arrange flour tortillas on a foil-lined baking sheet. Spray both sides lightly with oil. Broil the first side for about 1 minute, flip carefully, and broil the other side for an additional 30 seconds to 1 minute, watching very closely to avoid burning. Broil the tortillas just before assembling the tostadas to ensure they stay warm and crisp.
Assemble tostadas: Spread the vegetable mixture evenly over the crispy tortillas. Top with chopped carne asada, a sprinkle of cotija cheese, and a dollop of lime crema.
Serve: Arrange the tostadas on a serving platter. Add a lime wedge to each tostada and serve immediately. Enjoy!