Cut chicken into small bite-sized pieces and trim off any excess fat. Season with salt & pepper.
Cut lemongrass into thin slices until the purple rings disappear - this is where the flavor is!
Add the sliced lemongrass and garlic into a mortar and pestle and pound until at a paste-like consistency. Mince the shallots and Thai chilis and combine them with the other aromatics. (Alternatively, mince all 4 aromatics in a food processor).
In a small bowl, combine sugar, fish sauce, and oyster sauce.
Add 1-2 tsp olive oil to a large skillet and heat to medium-high heat. Pan fry the chicken for 3-4 minutes per side.
Add the aromatics to the skillet and stir to prevent burning. Sauté until fragrant, about 1-2 minutes.
Add the liquid sauce mixture into the skillet, coating the chicken pieces thoroughly.
Remove from heat and garnish with chopped cilantro. Serve with rice, sliced cucumbers, and a side of sweet chili sauce if desired.
Enjoy!