Preheat the oven to 375°F. Line a baking sheet with foil.
In a small bowl, stir together the breadcrumbs and milk. Let sit for 5 minutes.
In a large bowl, combine the breadcrumb mixture with the ground beef, eggs, scallions, garlic, 1 teaspoon kosher salt and 1/4 teaspoon black pepper.
Using your hands, scoop out 1 1/2-tablespoon portions of the meat mixture and roll it into balls. Place the meatballs on the prepared baking sheet, spacing them at least 1 inch apart.
Bake the meatballs until they are no longer pink in the center, 15 to 20 minutes. While the meatballs are baking, make the sauce:
In a small saucepan set over medium-low heat, whisk together the grape jelly and chili sauce until warmed.
Remove the meatballs from the oven and add them to a large bowl. Pour over the sauce and gently toss to coat.
Serve the meatballs topped with sliced scallions (optional).