Preheat the oven to 400°F and line a baking sheet or baking dish with parchment paper.
In a large bowl, mix together the ground beef, panko, soy sauce, ginger paste, minced garlic, green onion whites, and sriracha until just combined. Do not over mix.
Roll the mixture into meatballs, about 1 to 1½ tablespoons each, and place them on the prepared pan. Bake for 15 to 18 minutes, or until cooked through and browned.
While the meatballs bake, add the soy sauce, maple syrup, rice vinegar, gochujang or sriracha, garlic, ginger, and sesame oil to a small saucepan over medium heat. Stir and bring to a gentle simmer.
In a small bowl, whisk the cornstarch with 1 tablespoon water until smooth. Pour it into the sauce and stir for 1 to 2 minutes, until the sauce thickens and turns glossy.
Add the baked meatballs to the saucepan or transfer them to a bowl and pour the sauce over top. Toss until evenly coated, then top with the green onion greens before serving.