Step 1

Heat 2 tablespoons oil in a large skillet over high heat. Add onions and 1/4 teaspoon salt; cook, stirring frequently, until the onions begin to brown, about 5 minutes. Reduce the heat to low, add 2 tablespoons water and cover. Cook, stirring frequently until the pan cools down, and then occasionally, always covering the pan again, until the onions are greatly reduced and have a deep caramel color, 25 to 35 minutes.

Step 2

Meanwhile, rinse lentils and pick out any small stones; combine the lentils with the remaining 4 cups water in a soup pot or Dutch oven. Bring to a boil. Reduce heat to maintain a simmer, cover and cook for 20 minutes. Trim the white ribs out of the chard; chop the greens and slice the ribs (keep in separate piles). Cut potato into 1/2 -inch dice. Chop spinach; set aside.

Step 3

When the lentils have cooked for 20 minutes, stir in the chard ribs, potato, scallions, broth and the remaining 1 teaspoon salt; return to a gentle simmer. Cover and cook for 15 minutes.

Step 4

Stir in the chard leaves, broccoli, cumin and coriander. When the onions are caramelized, stir a little of the simmering liquid into them; add them to the soup. Return to a simmer, cover and cook 5 minutes more. Stir in the reserved spinach, cilantro, mint, jalapeno and pepper; return to a simmer, cover and cook until the spinach is tender but still bright green, about 5 minutes more. Stir in 1 tablespoon lemon juice. Taste and add more lemon juice and/or pepper, if desired. Garnish each bowl of soup with a drizzle of olive oil and crumbled feta cheese.