For the chicken:

1. In a food processor or blender, combine half of the pineapple, half of the onion (1/4 onion total), half of the jalapeño, and half of the lime juice with the garlic, chicken broth, tomato paste, spices, and salt. Purée until smooth.
2. Heat olive oil over medium-high heat in a dutch oven or heavy-bottomed pan with a lid (keep uncovered for now).
3. Pound chicken to tenderize, and season with salt and pepper on both sides.
4. Brown chicken breasts until golden brown, about 5-6 minutes per side.
5. Pour the puréed sauce over the chicken, reduce the heat to low, and cover. Cook for about 20 minutes, or until chicken is cooked through. (TIP: You can use this time while you wait to make the guacamole. See below.)
6. Remove the chicken from the sauce and transfer to a cutting board. Raise the heat to medium-high and let the sauce come to a boil. While the sauce reduces, shred the chicken using a fork.
7. When the sauce is reduced by about half, return the shredded chicken to the pot and toss to combine.

For the guacamole:

1. Dice remaining pineapple and mince remaining onion and jalapeño.
2. Mash avocados.
3. Mix in yogurt and remaining lime juice, then add salt to taste.
4. Mix in tomato, cilantro, onion, and jalapeño.