Peel and quarter the potatoes. Halve the fennel bulbs lengthwise, remove the stalk from each half, halve again, and cut into 1cm thick strips. Set aside the green fronds. Peel and finely chop the onions and garlic. Chop all the herbs together with the reserved fennel fronds.
In a bowl, combine the minced meat with salt, pepper, and paprika powder. Add the 2 eggs and mix until just combined.
Heat a large pan over medium heat. Add the onions and garlic and cook until translucent, about 5 minutes.
Add the fennel strips and potato quarters and cook for 2 minutes.
Add the chunky tomatoes and deglaze the pan. Stir in the herbs, stock grains, paprika powder, salt, and pepper. Simmer for 10 minutes, then taste and adjust seasoning.
Transfer the vegetable mixture to a baking dish. Shape the meat mixture into small meatballs and place them among the vegetables. Scatter the pine nuts and mozzarella on top.
Bake in a preheated oven at 160°C (320°F) for 35 to 40 minutes, until the meatballs are cooked through (internal temperature at least 74°C / 165°F).