Set your oven to 475°F so it's fully heated by the time your skillet is ready to go in. A hot oven is what gives the cheese that lightly crisped, golden top everyone loves. Don't skip this step or the bake will turn out soggy instead of bubbly.
Warm the olive oil in your oven-safe skillet over medium heat on the stovetop. Once it's shimmering, add the minced garlic and cook it for about two minutes, stirring often so it doesn't burn. You want it fragrant and just barely golden, not browned.
Stir the tomato paste right into the garlic and oil, keeping things moving for about a minute. The paste will darken slightly and smell rich and toasty as it cooks. This short step deepens the flavor far more than just dumping in cold paste later would.
Pour in the drained white beans along with the boiling water, then season generously with salt and pepper. Stir everything together until the beans are fully coated in that garlicky tomato mixture. The boiling water helps loosen the paste into a light, saucy coating.
Sprinkle the mozzarella and parmesan evenly over the top of the skillet, making sure to cover the beans completely. An even layer means every bite gets that melty, cheesy pull. Don't be shy here, since the cheese is really the star of the show.
Slide the skillet into your preheated oven and bake for 8 to 10 minutes, until the cheese is fully melted and just starting to crisp at the edges. If you want extra color, switch to broil for the last minute or two, watching closely so it doesn't burn. Pull it out once the top looks golden and irresistible.