Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a large bowl, combine ground meat, breadcrumbs, egg, onion, garlic, salt, and pepper. Mix until just combined.
Shape mixture into small meatballs (about 1–1.5 inches in diameter) and place on the prepared baking sheet.
Bake for 18–20 minutes, or until cooked through and golden brown.
While meatballs cook, make the glaze: in a saucepan, whisk together maple syrup, soy sauce, vinegar, garlic, mustard, and red pepper flakes. Simmer over medium heat for 5–7 minutes until slightly thickened.
Add cooked meatballs to the saucepan and toss until evenly coated.
Garnish with chopped parsley or chives and serve warm.