Heat the broiler to high.
Warm the olive oil in a large skillet over medium heat.
Add the onion and cook for 5–6 minutes until softened.
Stir in the garlic and red pepper flakes and cook for 1 minute.
Pour in the vegetable broth mixture and simmer until slightly reduced.
Add the chickpeas along with their liquid and simmer for about 3 minutes.
Stir in the kale, season with salt and pepper, and cook until the kale wilts, about 3–4 minutes.
Remove from the heat and fold in the chopped basil.
Arrange the sourdough slices on a baking sheet and broil for about 1 minute per side until golden.
Rub each toast with the cut side of the lemon.
Spoon the Kale and Chickpea Toasts mixture generously over each slice.
Sprinkle with grated Parmesan and drizzle lightly with olive oil before serving.