Thinly slice the chicken breasts into very thin 1/4" pieces. Add the sliced chicken, cornstarch, salt, and pepper into a bowl and mix together. Let the chicken sit for 10-15 minutes while you prepare the vegetables and sauce.
For the sauce, combine all the ingredients together in a bowl or liquid measuring cup and whisk until smooth. Cut the broccoli, carrots, and red bell pepper into small bite-sized chunks making sure that they are all roughly the same size.
Add another teaspoon or so of oil to the pan if needed and heat again until hot and rippling. Add the broccoli, carrots, red pepper, and pineapple to the hot skillet and cook, stirring often, until the vegetables are bright in color and barely tender. Add the 1/4 cup of the reserved pineapple juice to the skillet and cover with lid. Cook and let the vegetables steam for 2-3 minutes until crisp-tender.
Add the chicken back to the skillet. Whisk the sauce to recombine and then stir the sauce into the skillet and simmer for 2-3 minutes until slightly thickened.
Serve immediately over hot cooked rice of choice, or cauliflower rice.
If you don't have molasses you can replace it with honey. Or just don't add it at all. I've done that before. The molasses gives the stir fry an amazing, unexplainable flavor. So use it if you have it!
I use the tubes of garlic paste and ginger paste that you can find in the refrigerated part of the produce area in the grocery store. Super easy and provides so much fresh flavor.