Heat the olive oil in a large Dutch oven or pot over medium-high heat. Add the onion and jalapeño. Cook for 3 minutes until the onions begin to soften. Add the garlic and cook for 30 seconds until fragrant.
Add the masa harina and cook for 1 minute, stirring constantly.
Add the enchilada sauce, chicken broth, shredded chicken, black beans, diced tomatoes, diced green chiles, and salt. Stir together and cook for 10 minutes, uncovered, until the soup begins to simmer. Stir the soup occasionally to ensure the masa harina gets fully distributed throughout the soup.
Remove the pot from the heat and stir in the cream cheese until it is completely melted.
Serve in bowls garnished with shredded Monterey jack cheese, avocado slices, and cilantro.