Add broccoli to boiling water and cook 5 minutes, or until broccoli is bright green and very tender. Drain thoroughly in colander and return to pot. Trim and thinly slice green onion on an angle. While broccoli cooks, form meatballs.

Combine ground beef, 1/3 the panko, 1/3 the Parmesan cheese, 1/3 the liquid egg, 1/2 tsp. salt, and a pinch of pepper in a medium mixing bowl. Mix to combine and divide into six equal-sized balls. Press your thumb into center of each meatball and place a mozzarella ball into the well. Close meat around mozzarella, re-form into a ball, and place on one side of a prepared baking sheet. Form a tight seal so cheese stays inside meatball.

Using a potato masher or fork, mash broccoli until mostly smooth. Continue to mash while adding the remaining liquid eggs 1 Tbsp. at a time. This prevents eggs from scrambling on hot broccoli. Add remaining Parmesan cheese (reserve a pinch for garnish) and remaining panko and stir to combine. Season with 1/4 tsp. salt and a pinch of pepper. Using a tablespoon measure, scoop mix onto baking sheet next to sliders. Wipe pot clean.

Roast meatballs and broccoli tots 23-28 minutes, or until meatballs reach a minimum internal temperature of 160 degrees and broccoli tots are firm and browned on bottoms and edges. Cheese may leak out of meatballs while cooking - this is okay.

Arrange slider buns on second baking sheet and bake 2-3 minutes, or until toasted. Toast buns during last 5 minutes of roasting meatballs and tots so everything is ready at same time. Add pizza sauce to pot used for broccoli and place over medium heat. Bring sauce to a gentle boil, about 2-3 minutes, and remove from burner.

Place one meatball on each slider bun, top with a spoonful of sauce, and garnish with green onion and remaining Parmesan. Serve alongside broccoli tots.