Dice the cucumber, beef, bell peppers, and tomato.

Marinate the beef with soy sauce, oyster sauce, garlic, and sugar substitute.

Heat 1 teaspoon unsalted butter in a pan, add the beef and stir-fry until just cooked. Add the tomato and bell peppers, stir-fry until cooked to your liking. Add the cucumber, stir well, then turn off the heat.