If you have bone-in chicken thighs, cut around the bone to remove it. Discard the bones or save them for making chicken stock later (you can freeze the bones).
Chop the chicken thighs into 1 inch/2.5 cm cubes.
Add 1 tablespoon of soy sauce and 1 tablespoon of cornstarch to the cubed chicken meat. Mix until combined and the chicken is evenly coated with the marinade. Set aside while you prepare the rest of the ingredients.
Prepare the sauce
Mix the remaining soy sauce, salt, sesame oil, and sugar in a bowl. Combine the water and the cornstarch in a separate bowl to make a cornstarch slurry.
Chop the vegetables
Chop all the vegetables into similarly sized pieces. Cut the carrots and the bell pepper into thin strips, like thick julienne pieces.
Heat 1 tablespoon of canola oil in a wok or a pan over high heat.Once the oil starts to simmer, add the marinated chicken. Stir continuously until the chicken begins to turn golden on the outside, about 2 minutes. Remove from the pan and set aside for later.If you want to cook with a clean pan, rinse out the pan for the next steps.
Add the remaining canola oil to the pan over high heat. When the oil simmers, add the aromatics. Continuously toss the aromatics with a spatula to avoid burning them. Cook for about 30 seconds.
Add the broccoli florets to the pan. Stir the broccoli continuously and allow to cook for 2 minutes. If you have a lot of broccoli, you may need to add 1-2 tablespoons of water and cover with a lid to steam the broccoli.
Add the sliced carrots and bell peppers. Toss the vegetables with your spatula by pushing them to the side of your pan and folding them over. Continue to stir the vegetables until they are softened but still crunchy, about 3 minutes.
Add the cooked chicken back into the pan with the vegetables. Add the soy sauce-sesame oil mixture into the pan. Stir to combine.
Stir the cornstarch slurry in case the cornstarch has settled to the bottom of the bowl.
Make a well in the middle of the pan. Pour the cornstarch slurry into the pan.
Stir the vegetables into the cornstarch slurry mixture.
Continuously stir the vegetables until the cornstarch slurry thickens into a sauce that's about the consistency of gravy. The stir fry is ready when the gravy coats the back of a spoon.
Remove the stir fry from the heat and plate it. Serve it with rice or noodles.