Preheat your oven to 350°F.
In a skillet over medium heat, add olive oil and sauté the diced onions until they are translucent, about 3-4 minutes. Season with salt and pepper.
In a large mixing bowl, combine the sautéed onions, cut hot dogs, chili, mustard, and ketchup. Mix well until everything is evenly coated.
Place the slider buns in a baking dish, cut side up. Spoon the chili dog mixture evenly over the buns.
Sprinkle shredded cheddar cheese over the top of the chili dog mixture.
If using, add sliced jalapeños on top of the cheese.
Cover the baking dish with aluminum foil and bake for 15 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let cool for a few minutes before serving.