Tomato and Zucchini Frittata

Bahan-bahan (4 porsi)

• 2 tsp olive oil
• 1 medium onion (diced)
• 1 -1/2 cups zucchini (diced into matchsticks, 7 oz total)
• 5 large eggs
• 2 large egg whites
• 1/4 cup Asiago cheese (grated)
• kosher salt and fresh pepper (to taste)
• 2 medium vine ripe tomatoes (about 8 oz, cored and thinly sliced crosswise)