Summer Squash Skillet

Found in SL August 2024 issue here

2 Tbsp. olive oil
2 large (12 oz. each) zucchini, cut into 1/4-in.-thick slices (about 5 1/2 cups)
1 large (12 oz.) yellow squash, cut into 1/4-in.-thick slices (about 2 1/2 cups)
1 medium-size (8 oz.) yellow onion, thinly sliced (about 2 cups)

1 tsp. kosher salt, plus more to taste 
1/2 tsp. black pepper
1/4 tsp. crushed red pepper
7 oz. Gruyère cheese, shredded (about 1 3/4 cups), divided
1/3 cup panko (Japanese-style breadcrumbs) 
1 tsp. grated lemon zest (from 1 lemon)

Preheat oven to 400℉. Heat oil in a 12-inch cast-iron skillet over medium-high. Add zucchini, squash, onion, salt, and black pepper. Cook, covered, stirring occasionally, until squash mixture is mostly tender, about 10 minutes. Uncover and cook over medium-high, stirring occasionally, until tender and most of the liquid has evaporated, about 5 minutes.

Remove from heat, and fold in crushed red pepper and 1 cup of the Gruyère. Stir together panko, lemon zest, and remaining 3/4 cup Gruyère in a small bowl; sprinkle evenly over squash mixture. Bake in preheated oven until golden on top, about 18 minutes.