Place cold water in a large pot. Add diced onion and carrots. Bring to a boil, then reduce heat, cover with the lid and simmer for 10 minutes. Add diced bell pepper and potatoes to the pot. Simmer for another 10 minutes.
Sauté the tomatoes
In a separate saucepan, sauté chopped tomatoes in olive oil for 5 minutes to enhance their flavor. Set aside.
Prep and add the runner beans
Wash, top, and tail runner beans. Cut into one-inch pieces. Check if potatoes are cooked (they should be tender). Add runner beans and vegetable broth to the pot. Simmer for 2-3 minutes.
Finish the soup and serve
Finish by stirring in sautéed tomatoes and salt. Taste and adjust seasoning. Remove from heat and garnish with fresh parsley and lovage if using.