Heat oil over medium-high heat in a large soup kettle. Add onion and sauté until translucent, about 5 minutes. Add pasta, tomato sauce, 1 quart of water, beans, roasted red peppers, smoked paprika, and oregano. Cover and simmer until pasta is almost tender and most of the liquid has absorbed, 8 to 10 minutes, depending on pasta shape. Stir in spinach and optional feta and cilantro until spinach has wilted. Re-cover pot and continue to cook until liquid has absorbed and pasta is tender just a few minutes longer. Serve with an additional sprinkling of cheese, if you like.