In a large pot, sauté the onions and garlic until fragrant.
Add the diced tomatoes, shrimp paste, and broth. Bring to a simmer.
Add the crab meat and tofu to the pot. Season with fish sauce, sugar, salt, and pepper. Let it simmer for about 20 minutes.
While the broth simmers, cook the rice vermicelli noodles according to package instructions. Drain and set aside.
To serve, divide the cooked noodles into bowls. Ladle the hot broth over the noodles.
Garnish with fresh herbs, lime wedges, bean sprouts, green onions, and chili slices.
Serve hot and enjoy!