Heat oven to 425°F and line a sheet pan with parchment. Mix beef, grated onion, egg, panko and salt and shape into twenty even meatballs; arrange on the pan.
Bring rice and 1 3/4 cups water to a boil in a saucepan. Cover, reduce heat to low and cook for 18 minutes, then rest off heat, covered, for 10 minutes.
Bake meatballs for 14 to 17 minutes until browned and 160°F at their centers.
Combine soy sauce, mirin, sake, sugar and ginger in a small saucepan. Simmer uncovered for 8 to 12 minutes until reduced to about 1/2 cup and lightly syrupy, watching closely near the end.
Heat oil in a skillet over medium-high heat. Add carrots, snow peas and 3 tablespoons water, cover for 2 minutes, then uncover and cook for 1 minute until the water evaporates.
Toss the cooked meatballs with the teriyaki sauce. Divide rice and vegetables among four bowls and add five meatballs to each, spooning the remaining glaze over them.