Use a 6-quart slow cooker.

To create the soup base, add the broth, lime juice, lime zest, sugar, fish sauce, ginger, and coconut milk into the slow cooker insert and stir.

Add the red chili paste, ½ teaspoon at a time, until you have reached the desired heat. (I use about 1½ teaspoons. You can always add more after cooking, though, so don’t overdo it.)

Add the tofu, bell pepper, garlic, mushrooms, and tomatoes to the insert. Stir carefully so you do not break up the tofu or the tomatoes.

Cover and cook on low for 4-5 hours, or on high for 2-4 hours. The soup is finished when it is fully hot, and the flavors have combined nicely.

When in doubt, use the shortest amount of cooking time and put the slow cooker on the warm setting until you are ready to serve. Garnish with lime slices.