Heat oil in large non-stick skillet over medium-high heat.

Cook onion, zucchini, garlic, 1 tsp. kosher salt and 1/2 tsp. pepper until mixture is softened and golden, stirring occasionally, about 12-14 minutes.

Stir in basil.

Meanwhile, in bowl combine eggs, mozzarella and remaining 1 tsp. kosher salt and 1/2 tsp. pepper. Pour egg mixture over vegetables in skillet. Reduce heat to medium-low and cook until eggs are almost set.

Dollop pesto over top and swirl. Top with tomatoes, reduce heat to low and cook, covered, until frittata is cooked through.