Heat 2 tablespoons olive oil in a Dutch oven or large pot over medium-high heat until shimmering. Add 1 diced medium yellow onion, 2 peeled and diced large carrots, 1 peeled and diced medium sweet potato, and 1 teaspoon kosher salt. Cook, stirring occasionally, until softened and beginning to brown, 7 to 10 minutes.
Stir in 3 minced garlic cloves, 1 tablespoon tomato paste, and ¼ teaspoon red pepper flakes if using. Cook, stirring frequently, until the paste is darkened in color, about 1 minute. Stir in 1 (32-ounce) carton low-sodium vegetable broth, 1 (about 15-ounce) can fire-roasted diced tomatoes and their juices, 1 (about 15-ounce) can drained and rinsed chickpeas, and 1 teaspoon dried oregano. Bring to a boil. Reduce the heat to maintain a simmer and cook for 15 minutes.
Stir in 1 small bunch chopped kale leaves and 8 ounces cut green beans. Simmer until the green beans are tender, about 15 minutes. Turn off the heat. Stir in ½ cup coarsely chopped fresh herbs and 1 tablespoon lemon juice. Taste and season with more kosher salt as needed.
