Heat the sesame oil in a stockpot over medium-high heat; add the chicken, lemon juice, and soy sauce; cook and stir until the chicken is cooked through, 3 to 5 minutes.
Whisk together the coconut milk, curry paste, and flour in a bowl until smooth; pour into the skillet.
Add the bell pepper, sweet onion, red onion, garlic, potatoes, bamboo shoots, water chestnuts, and mushrooms; reduce heat to low, cover, and simmer 45 minutes. Stir in cilantro and remove from heat.