Casseroles can be for summer too! We packed this one with peak-season vegetables—corn, zucchini and tomatoes—then topped it with crispy tater tots and gooey melted cheese, making it a dinner winner.
Preheat oven to 450°F.
Heat oil in a large ovenproof skillet over medium-high heat. Add beef and onion. Cook, breaking up the beef with a wooden spoon, until the onion is soft and the beef is no longer pink, about 5 minutes. Add zucchini, 1 cup tomatoes, corn, chili powder, Worcestershire and salt; cook, stirring, until the zucchini has begun to release its liquid, about 3 minutes. Sprinkle with flour and cook, stirring, until the liquid has thickened, about 1 minute more. Remove from heat.
Spread the mixture into an even layer. Sprinkle with 1/2 cup cheese and arrange tots evenly over the cheese. Coat the tots with cooking spray. Transfer the pan to the oven.
Bake for 15 minutes. Sprinkle with the remaining 1/2 cup cheese and bake until the cheese is melted and the tots are golden brown, about 5 minutes more. Top with the remaining 1/2 cup tomatoes and garnish with chives, if desired.