Sheet Pan Masala Egg Sandwiches

Name: Sheet Pan Masala Egg Sandwiches
Ingredients: Neutral oil, for oiling the pan; 10 large eggs; 3/4 cup heavy cream; 1 1/4 teaspoons ground turmeric; 1 teaspoon cumin seeds; 3/4 teaspoon garam masala; 1/2 teaspoon Kashmiri chili powder, paprika, or hot paprika; 1 teaspoon kosher salt; 3 cups baby spinach (about 3 ounces); 1 medium bunch fresh cilantro; 2 medium scallions; 1 to 2 serrano chiles; 6 ounces sharp cheddar cheese (1 1/2 cups shredded); 1 large tomato; Flaky salt; Freshly ground black pepper; 8 English muffins; 3 tablespoons unsalted butter; 8 slices American cheese