Prepare the tamarind: If using tamarind pods, soak 3-4 pods in 1 cup warm water for 15 minutes, then squeeze and strain to extract the pulp, discarding seeds and fibers. Set aside the tamarind water.

Cut the fish into 2-inch chunks and pat dry with paper towels. Season lightly with salt and black pepper. Set aside.

Dice tomatoes into wedges, cut pineapple into bite-sized chunks, slice celery diagonally, and cut the base off bean sprouts if using.

In a large pot or Dutch oven, heat vegetable oil over medium-high heat. Add minced garlic and sliced onions, sauté for 2-3 minutes until fragrant and softened.

Add diced tomatoes to the pot and cook for 3-4 minutes until they begin to break down and release their juices.

Pour in 6 cups of water or fish stock, then add the tamarind water, fish sauce, and sugar. Stir well to combine. Bring to a boil.

Once boiling, add the pineapple chunks and sliced celery. Reduce heat to medium and simmer for 5 minutes.

Taste the broth and adjust seasoning - add more fish sauce for saltiness, sugar for sweetness, or tamarind for sourness to achieve the perfect balance.

Gently add the fish chunks to the simmering broth. Do not stir vigorously to keep the fish pieces intact. Cook for 5-7 minutes until the fish is just cooked through and opaque.

Add bean sprouts if using and cook for 1 minute more. Remove from heat.

Stir in fresh cilantro, Thai basil, and sliced chili peppers. Taste and adjust final seasoning if needed.

Serve immediately in large bowls over steamed white rice, ensuring each serving gets fish, vegetables, and plenty of aromatic broth.