On a baking sheet, place the 4 potatoes. Using a fork, puncture holes all around the potatoes. Bake for 1 hour until the potato gives when you press into it.
In a pan, heat 1 tablespoon of olive oil. Add the onions and cook until golden.
Add the garlic, broccoli, salt, and pepper, and cook until the broccoli is tender. Scoop mixture into a bowl.
Add the cream cheese and cheddar cheese to the bowl of broccoli and stir to combine. Set aside.
Once the potatoes have cooled, place one on a cutting board. Cut the potato in half lengthwise. Cut off one of the ends of the potato. Using a spoon, scoop out the insides of the potato making sure not to scoop out too much or the potato skin will be too thin. With the remaining potatoes, cut them in half lengthwise and cut off both of the ends and scoop out the potato.
On a parchment paper-lined baking sheet, place both ends. Place three of the skins alongside one potato end and place the other 3 potato skins alongside the other end
Brush the potato skins with the rest of the olive oil and season with salt and pepper.
Scoop the broccoli cheddar mixture into the potato skins and press down into an even layer. Sprinkle the rest of the cheddar cheese and mozzarella cheese over the potato skins. Bake for 5 minutes until melted.