Make the chickpeas and tomatoes: In a medium skillet over medium heat, heat the oil until shimmering. Add the onion, fennel seeds, garlic powder, salt and pepper, and cook, stirring occasionally, until the onions start to soften and turn translucent, about 5 minutes. Add the chickpeas and tomatoes, let it come to a simmer, and cook, stirring occasionally, until the liquid reduces and the flavors meld, 7 to 10 minutes. Taste, and season with more salt and/or pepper, if needed.
Make the polenta: Meanwhile, in a medium saucepan over high heat, bring the water or broth to a boil. While whisking steadily to prevent lumps, slowly pour in the cornmeal. Whisk in the salt, reduce the heat to low, so the liquid is at a gentle simmer, cover partially (to protect from eruptions), and cook, stirring occasionally, until thickened, about 10 minutes. Stir in the butter, a piece at a time, until fully incorporated. Taste, and season with more salt, if needed.
To serve, divide the polenta among 4 bowls and top with the chickpea and tomato mixture.
