Place the soy sauce, honey, plum preserves, chicken stock, cornstarch, ginger, sriracha, garlic and scallions in a mason jar. Secure the lid and shake until everything is combined. Set aside.
Heat the peanut oil in a large skillet over a medium-high heat. When the oil is hot, add the chicken and cook for 2 minutes, then remove and set aside. Add the onions, broccoli and cauliflower and cook until the veggies have softened but still have a bite, 4 to 5 minutes.
Return the chicken to the skillet and pour over the sauce. Stir everything together and cook until the sauce is very thick, 1 to 2 minutes. Add a little water if needed to make it more saucy.
Serve the stir-fry over cooked rice. Garnish with some sliced scallions and sesame seeds. Enjoy.