Preheat grill to medium heat and lightly oil the grate.
Grill 2 skinless boneless chicken breast halves until dark grill marks appear and they are no longer pink inside, about 5 minutes per side.
Let the chicken breasts cool, then place them in a bowl and coarsely shred with 2 forks.
Bring a large pot of lightly salted water to a boil.
Cook 1 cup of uncooked orecchiette pasta in the boiling water, stirring occasionally until cooked through but firm to the bite, 5 to 8 minutes.
Drain the pasta and return it to the pot.
Stir the shredded chicken, 1 cup of tomato pasta sauce, 1/2 cup of cut broccolini, 1/2 can of stewed drained tomatoes, 1/3 cup of sliced portobello mushrooms, 2 tablespoons of minced garlic, and 2 teaspoons of crushed red pepper flakes into the cooked pasta.
Place the pot over medium heat and cook, stirring frequently, until the mushrooms and broccolini are cooked through and tender, 5 to 10 minutes.