Cut the steak lengthwise in half and slice each half across at an angle into 2 inch wide triangles.
Combine 2 tbsp olive oil, garlic, sugar, soy sauce, thyme and 2 tsp harissa sauce into a zip bag (or large bowl) and add beef. Close the bag and mix by squeezing the bag with your fingers to coat all the beef pieces (or toss in bowl to coat each piece and cover). Marinate at room temperature for 30 minutes, or refrigerate at least 2 hours (or up to overnight), mixing occasionally.
Drain the beef. Divide and cook in two batches in a large skillet (or cook them in two skillets simultaneously - preferred). Add 1 tbsp olive oil to the skillet and heat on high. Add beef, taking care not to overcrowd. Cook until well browned on all sides for a total of 6 - 7 minutes for medium rare.
Whisk 2 tbsp olive oil, 1 tbsp harissa and 2 tbsp water in a small bowl to blend. Season this sauce with salt.