Mix 3 Tbsp. soy sauce, 2 Tbsp. brown sugar, 1 Tbsp. oyster sauce, 2 Tbsp. ginger garlic paste and 3/4 to1 Tbsp. Sirracha together in a small bowl
Heat peanut oil in a skillet over medium heat. Add chicken thighs. Brown for a few minutes. Add sauce. Turn down to low & simmer, covered, until the chicken is cooked through. (I like to cook it until it is falling off the bone - 1.5 hours or more). Remove from heat & set aside.
Bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water until cooked through but firm to the bite, about 12 minutes; drain and transfer to a large bowl. Drizzle sesame oil over the spaghetti; toss to coat. Place a plate atop the bowl to keep the noodles warm.
Shred the chicken & set aside. Discard cooking liquid.
If using frozen veggies, put them in the microwave for a couple of minutes to thaw them out.
Heat 1 Tbsp. peanut oil in a wok or large skillet over medium-high heat. Add mixed vegetables to the skillet; cook and stir until slightly tender, about 3 minutes. Stir chicken into the vegetable mixture; cook and stir until the meat is cooked through, about 5 minutes.
Mix remaining soy sauce, brown sugar, oyster sauce, ginger garlic paste and Sirracha together in a small bowl. Add spaghetti and sauce to the wok with the vegetables and chicken; cook and stir until the spaghetti is hot, 2 to 3 minutes.