Melt butter in a large soup pot over medium-high heat. Add chicken, bell pepper, and shallots, season with salt and pepper, and then saute until vegetables are tender, 5 minutes. Add garlic then saute for 1 more minute. Add chicken broth, 1-3/4 cups milk, Rotel and chili powder to the pot then turn heat up to high and bring to a simmer. Add rice then turn heat down to medium-low, place a lid on top, and then cook until rice is al dente, stirring occasionally. Stir remaining 1/4 cup milk into flour in a small dish then drizzle into the soup and simmer uncovered for 5 minutes. Remove pot from heat then slowly sprinkle in cheese while continuously stirring to make sure it melts evenly. Let soup sit and thicken for 10 minutes before serving with crushed tortilla chips.