Mini Tater Tot Sliders

35min · 16 servings 32 frozen potato rounds (such as Ore-Ida® Crispy Crowns®) 2 tablespoons vegetable oil 8 ounces ground beef (85% lean) ¼ pinch kosher salt ¼ teaspoon black pepper 4 slices American cheese 1 tablespoon ketchup, or to taste 1 tablespoon mustard, or to taste 16 pickled gherkins, drained 16 toothpicks