In a large saucepan over medium heat, warm a glug oil. Add onion and a strong pinch of salt. Cook, stirring occasionally, until onion has beginning to soften (~ 5 minutes).
Mash ¼ cup of the chickpeas. Add them, along with the garlic, and continue to cook, stirring occasionally, until onion and garlic are both very soft and just beginning to brown around the edges (~ 5 minutes longer)
Add rosemary and red pepper flakes and cook, stirring, until fragrant (~ 30 seconds)
Add the chickpeas and tomatoes and cook, stirring occasionally, until tomatoes are slightly thickened (~ 8-10 minutes)
Add pasta and 4 cups of water. Increase heat to medium-high, bring to a simmer, and cook, until pasta is al dente, 13–16 minutes depending on the shape. Stir occasionally to prevent pasta from sticking,
Stir in parsley and Parmesan; season with another pinch salt and a grind of black pepper.
Divide brothy pasta between bowls. Drizzle with a little more oil and top with Parmesan and a sprinkle of fresh parsley