Heat olive oil in a large pot over medium heat. Stir in onion and garlic; cook and stir until the onion has softened and turned translucent, about 5 minutes. Stir in sweet potato, bell pepper, chicken, tomatoes, and 2 cups of water. Season with salt, chili powder, cumin, oregano, cocoa powder, cinnamon, and red pepper flakes. Increase heat to medium-high and bring to a boil. Dissolve flour in 2 tablespoons water, and stir in to boiling stew. Reduce heat to medium-low, cover, and simmer until the potatoes are tender but not mushy, 10 to 20 minutes. Stir the stew occasionally to keep it from sticking.