Season your chicken breast with salt and pepper and roast in a 420 degree oven for 45 minutes. While the chicken is roasting dice your onion, and poblano pepper and mince the garlic. Saute the onion, and poblano pepper in the olive oil until tender and then add the garlic and cumin and continue to cook for a minute or so. Add the chicken broth and potatoes and simmer for 15-20 minutes until the potatoes are just tender. Take the chicken meat off the bones and shred it and add it to the pot with the diced tomatoes, cilantro and Cotija cheese. Warm through and serve.