Place a wire rack inside a large cookie sheet. Spray both with cooking spray. (For easier cleanup, you can line the cookie sheet with aluminum foil first. Preheat your oven to 400°.
Combine the ground beef, oats, eggs, onion, milk, salt, pepper, red pepper flakes, worcestershire, ketchup, and parsley in a large mixing bowl. Mix thoroughly until well combined. (I like to use my hands, but you can use a heavy duty wooden spoon.) For tender meatballs, don't overmix.
Shape the meatball mixture into equal-sized meatballs. I used a 1 1/2 tablespoon scoop for portion control.
Arrange the meatballs on the prepared baking sheet. Bake at 400 degrees for 13-15 minutes, or until they are cooked all the way through. The internal temperature should be close to 165°.
Sauce
While the meatballs are cooking, prepare the sauce. Whisk together the chili sauce and jelly in a small bowl until smooth. Set aside.
Transfer the cooked meatballs to a large pot. Add the sauce and heat over medium heat, stirring occasionally, until heated through.
Notes
If you don't have jalapeno jelly, you can replace it with another flavor of jam and add 1/2-1 teaspoon of red pepper flakes or a few teaspoons of hot sauce.
To make the meatballs in a crockpot, place the hot cooked meatballs and sauce in your slow cooker and cook on high for about an hour, or until heated through. You can also cook them on low for 2-3 hours, or use the warming setting to keep them hot until you are ready to serve them.
Leftover meatballs can be stored in an airtight container in the refrigerator for 4-5 days.