Start with the sauce: Rough chop tamarind and remove pits as you find them. Combine the tamarind and warm water in a small bowl. Set aside for 5-10 minutes to soften as you wash and trim the stir-fry vegetables.
Once the tamarind has softened, mash and stir with a fork to create tamarind juice. Once all the tamarind is incorporated in the water, strain and discard the skins, pits etc. left in the strainer.
If using fresh chillies, take a peek at this video if you are not familiar with preparing hot chillies. Thai chillies are HOT!! http://www.bbcgoodfood.com/technique/how-prepare-chillies
Combine all sauce ingredients in a small saucepan. Heat on medium heat stirring often until sugar is dissolved and sauce is simmering. Simmer until it reduces by 1/3 (15 minutes or so). Remove from heat, put a lid on the pot and set aside. If you are using noodles, prepare them now according to the package directions.
Once the sauce is heating on the stove, chop all the vegetables stir-fry style and set aside. Mince garlic and set aside. Slice the steak thinly into stir-fry sized pieces and begin heating your pan or wok until almost smoke point. Stir-fry the meat in small, quick batches, keeping the wok hot, so the meat stays tender. Cook it just enough to sear the outside and keep the inside medium-rare. Remove each batch from the wok and set aside. Add more oil/fat as needed.
Once the meat is all cooked and set aside, add a bit more oil to the wok, add garlic and fry until just browning, then add the vegetables. When the vegetables are nearly done, add the meat back in and stir it all together. If you like some crunch to your noodles, remove the stir-fry from the wok at this point, fry the noodles and then combine everything back in the wok with the sauce. Otherwise, add noodles or spaghetti squash and sauce and let it cook briefly, stirring constantly to help noodles absorb the sauce but not scorch the sauce. If using rice, place a small portion of rice in the bottom of each bowl and top with stir-fry making sure to add a scoop of the delicious sauce to each bowl!! Add garnishes to taste. Enjoy!!