Place 1 pound boneless, skinless chicken breasts in the slow cooker. Add 3 cups salsa (no sugar added), 1 teaspoon ground cumin, 2 tablespoons chili powder, 1/2 cup corn kernels, 1/2 cup black beans, and 1/2 cup low-sodium chicken broth. Stir to combine and coat the chicken.
Cover and cook on low for 8 hours or on high for 4 hours, until the chicken is tender.
Remove the chicken from the slow cooker and shred it with two forks.
Return the shredded chicken to the slow cooker, stir to combine with the sauce, cover, and cook an additional 30 minutes on low or 15 minutes on high.
Warm 8 whole-wheat flour tortillas (in a dry skillet, microwave, or oven) while the chicken finishes.
Divide the shredded chicken among the tortillas (about 2 tablespoons per tortilla). Top each with the following, divided evenly: 1 cup shredded romaine lettuce, 1 large diced tomato, 1 cup shredded low-fat cheddar cheese, 1/4 cup diced avocado, and 1/4 cup plain Greek yogurt.
Fold or roll the tortillas and serve immediately.