In Multipurpose or Round Steamer, whisk together seasoning, coconut milk, tomato paste, and butter. The sauce will be thick. Add chicken breasts; press down firmly and flip to coat with some of the sauce. Cover; microwave on high, 9 min, or until cooked through.
Meanwhile, prepare yogurt sauce. Discard cilantro stems. Coarsely chop leaves; place in a bowl. Stir in yogurt and lemon juice. Taste and season with salt and pepper.
Once chicken is cooked, let rest 2 min, then uncover. Remove chicken to a cutting board. Using 2 forks, shred chicken. Stir back into sauce (in steamer), including any juices on the cutting board.
Divide chicken mixture on bottom half of each bun; spread top bun with yogurt sauce, then cover.