Place beef in a large skillet over medium heat; cook and stir until browned, about 8 minutes. Transfer to a plate lined with paper towels to drain excess grease.

Heat oil in a large skillet over medium-high heat. Add onion, tomatoes, green onions, 3 tablespoons soy sauce, 1/2 the lemon juice, garlic, beef bouillon, and black pepper. Cook and stir until flavors combine, 2 to 3 minutes. Stir in water chestnuts and green beans; cook and stir until tender, 8 to 10 minutes.

Stir drained ground beef, remaining 1 tablespoon soy sauce, and lemon juice into the skillet. Pour in coconut milk slowly; add chile pepper. Reduce heat to low and simmer until coconut milk is heated through, 2 to 3 minutes. Remove from heat.