Heat oil in a large saucepan over medium heat. Add onion and sauté until softened, about 4 minutes, stirring often. Add garlic and stir for another minute. Add salt, chickpeas, and vegetable stock. Bring to a boil, cover, reduce heat, and simmer 15 minutes.
Meanwhile, cook udon noodles in boiling water according to package directions. Cook broccoli (and cauliflower, if using) in boiling water until softened. Drain broccoli/cauliflower and pasta, reserving ¼ cup of the pasta water.
Place chickpea mixture in Vita-Mix. Add lemon juice and reserved pasta water and blend until smooth.
Combine chickpea sauce, pasta, broccoli/cauliflower, in a saucepan or large bowl and toss to combine. Serve warm, topped with grated parmesan cheese (or nutritional yeast flakes for vegans).
