For the toasts: Put an oven rack in the center of the oven. Preheat the oven to 400 degrees F.
Arrange the bread slices in a single layer on the baking sheet and drizzle with olive oil. Bake until light golden, about 10 minutes. Cool for 2 minutes. Rub the warm toasts with the cut side of the garlic. Set aside.
For the topping: In a large skillet, heat the oil over medium-high heat. Add the garlic and red pepper flakes and cook until the garlic is fragrant, about 30 seconds. Add 1/2 of the spinach and stir until it begins to wilt, about 2 to 3 minutes. Add the remaining spinach and cook until wilted, about 2 minutes. Season with salt, to taste. Using tongs, arrange the spinach on top of the toasts. Sprinkle with cheese and bake for 5 to 8 minutes until the cheese is melted and bubbling. Season with salt and cool for 2 minutes.
In a heavy 5 or 6 quart saucepan, heat the oil over medium-high heat. Add the pancetta and cook, stirring frequently, until brown and crispy, about 6 to 8 minutes. Using a slotted spoon, remove the pancetta and drain on paper towels. Set aside. Add the carrots, celery, onion, garlic, 1 teaspoon salt and 1 teaspoon pepper and cook until the onion is translucent, about 5 minutes. Stir in the chicken stock, basil, tomato paste, thyme, and bay leaf. Add the cubed baked chicken. Bring the liquid to a simmer. Reduce the heat to medium-low and simmer. Add the artichokes and the cannellini beans and simmer until liquid has reduced slightly, about 10 to 15 minutes. Remove the bay leaf and discard. Season the spezzatino with salt and pepper, to taste. Ladle the spezzatino into bowls and garnish with the cooked pancetta.