Start by heating 1 tablespoon of olive oil in a non-stick skillet over medium heat. Add the sliced red onions and sprinkle with granulated sugar. Sauté until the onions are caramelized and golden, about 7-10 minutes. Stir in the balsamic vinegar and crushed red pepper flakes, then set aside.
In the same skillet, season the chicken breasts with salt, pepper, and dried thyme. Add the remaining olive oil and cook the chicken over medium heat until golden brown and cooked through, about 6-7 minutes per side. Once cooked, let the chicken rest for a few minutes before slicing it thinly.
In a bowl, combine the thawed and drained spinach with mayonnaise and minced garlic. Mix until well combined. This creamy mixture will add richness to our panini.
Preheat your panini press or grill pan. Roll out the pizza crust on a lightly floured surface and cut it into rectangles or squares, depending on your desired sandwich size. Spread a layer of the spinach mixture on one half of each piece of crust. Top with sliced chicken, caramelized onions, and two slices of provolone cheese. Fold the crust over to create a sandwich.
Place the assembled panini on the preheated press or grill pan. Cook until the crust is golden and crispy, and the cheese is melted, about 3-5 minutes. If using a grill pan, press down with a spatula to achieve those lovely grill marks.
Slice the panini in half and serve immediately. The combination of warm chicken, creamy spinach, and gooey cheese is sure to make your taste buds dance.
