Garden Vegetable Frittata

2 tablespoons olive oil, plus more for drizzling 5 small red potatoes, thinly sliced 1 bunch green onions, trimmed and sliced 1 cup grape tomatoes, sliced 1 cup baby spinach, torn 1 clove garlic, crushed 8 eggs 1 tablespoon chopped fresh basil, plus more for garnish 1 to 2 cups shredded Asiago cheese, plus more for garnish Kosher salt and freshly ground black pepper