Add garlic through water into a mixing bowl. Whisk to combine. Place sirloin slices in a large ziplock bag and add 1/2 sauce. Seal and shake. Marinate for 1-3 hours.
Heat a large saute pan or wok to medium-high heat. Add oil. When oil is shimmering, add sirloin, saving the marinating juice. Allow to sear on each side to a golden brown, approximately 1 minute per side. Remove sirloin from pan and deglaze with a few tablespoons of water, scraping the brown bits at the bottom of the pan.
Add carrots and cover pan with a lid for 3-4 minutes. Check to prevent burning. Remove lid and add remaining veggies as well as remaining sauce, marinating juice and 1/2 teaspoon sea salt. Stir to combine and cook for 4-5 minutes or until veggies are al-dente (still some texture when you bite). Add sirloin back into pan and cook mixture another 2 minutes.
Serve stir fry over rice, cauliflower rice, black bean noodles like the brand recommended in the post, or zucchini noodles.
**Note: If you want to use other veggies than peppers and cabbage, that's totally cool! Just keep it to about 5 cups all together, and adjust the saute time accordingly.