Preheat oven to 400 degrees F. Combine all ingredients, except the marmalade and red pepper flakes, in a large bowl and mix until just combined. Moisten hands, gently form mixture into 1-inch meatballs (you should have about 25) and place on a baking sheet. (Meatballs can be made up through this step to 24 hours ahead and stored covered in the refrigerator; let come to room temperature 10 minutes before roasting.)
Bake until meatballs are warmed through and almost cooked, about 15 minutes. Meanwhile, stir together marmalade and red pepper flakes, and season with salt, as desired.
Remove meatballs from oven, toss with marmalade, return to oven and bake until the meatballs are completely cooked and the sauce is warmed through, about 5 more minutes. Skewer meatballs with toothpicks and serve.