Trim, peel, halve, and slice the onion. Thinly slice the garlic. Heat 1 tablespoon oil in a medium saucepan over medium heat. Add the onion and garlic and sprinkle with salt, pepper, smoked paprika, and cumin. Cook, stirring occasionally until the vegetables soften, 3 to 5 minutes.
Add 3 cups water to the pot with the vegetables. Scrub, trim, and quarter the potatoes. Add them to the pot and bring to a boil; lower the heat so the water bubbles steadily, cover, and cook, stirring occasionally until the potatoes are just tender, 10 to 15 minutes.
Rinse the chard and strip the leaves from the center ribs. Chop the ribs, add them to the pot, and stir. Cut the leaves crosswise into ribbons and reserve. Rinse and dry the parsley and mint; trim the toughest stems from the parsley and chop the leaves; strip the mint leaves from the stems and chop them.
Break the pasta into 2-inch lengths. Put the remaining tablespoon oil in a medium skillet over medium heat. When the oil is hot, add the pasta pieces and lower the heat to medium-low. Cook, stirring almost constantly and adjusting the heat as necessary, until the pasta is browned but not burned, 5 to 7 minutes. Transfer the fideos to a bowl and sprinkle with a little salt.
Drain and rinse the fava beans in a colander. Add the beans and chard leaves to the pot with the vegetables and cook, stirring occasionally until the leaves are tender, 2 or 3 minutes. Slice the caper berries. Taste and adjust the seasoning of the stew. To serve, ladle the stew into bowls and sprinkle the fideos on top. Garnish with the chopped parsley, mint, and sliced caper berries.