Kosher salt
12 ounces broccoli rabe (about 1 1/2 bunches), tough stems discarded, coarsely chopped
3 tablespoons olive oil, divided
2 large garlic cloves, minced
Pinch red pepper flakes
1/4 cup green olives, pitted and finely chopped
1 1/2 tablespoons drained brined capers, finely chopped
1 tablespoon red wine vinegar
4 Individual-size sandwich rolls, split (I like rolls with sesame seeds for this, but you do you)
1 pound fresh mozzarella cheese, sliced

Pour water into a large saucepan to fill about 1-inch and bring to a boil over high heat. Add a large pinch of salt and then the broccoli rabe and cook, stirring occasionally, until bright green and slightly wilted, about 30 seconds.
Drain the broccoli rabe in a colander, wipe the pot dry, and return it to high heat. Add 2 tablespoons of the oil, the garlic, and the red pepper flakes and stir until the garlic is fragrant, about 15 seconds. Immediately add the drained broccoli rabe and a large pinch of salt and cook, stirring, until the broccoli rabe is coated with the garlicky oil and is a bit more softened, about 3 minutes. Remove from the heat and set the broccoli rabe aside to cool down a bit.
Place the olives, capers, vinegar, remaining 1 tablespoon oil, and a small pinch of salt in a small bowl and stir to combine. Place the rolls, cut-side up, on a work surface and evenly distribute the olive mixture among the rolls, putting some on both halves of each roll. Divide the mozzarella and broccoli rabe evenly among the rolls, close the rolls, and then tightly wrap each sandwich in plastic wrap.
Place something flat and heavy on top of the sandwiches, such as a large cast-iron skillet. Let the sandwiches sit under this weight for at least an hour before eating or putting them in your backpack.