Put zucchini in large Dutch oven with a few inches of water. Simmer zucchini over medium-low heat until tender when poked with a fork, about 20 minutes. Use a slotted spoon to transfer zucchini to a blender, leaving about 1 inch of water in the bottom of the pot.
Blend zucchini until no large chunks remain; return to the pot. Combine bell pepper, red onions, and cilantro in the blender; blend until no large pieces remain. Stir bell pepper mixture into the blended zucchini; add cream, Swiss cheese, salt, and pepper. Cook over medium-low heat until warmed through and the cheese is melted, 5 to 7 minutes.