Cook the celery, carrot and onion in the olive oil in a large saucepan over medium heat until soft, about 5 minutes. Add the oregano, cumin, red pepper flakes, celery seeds and garlic and cook until fragrant, about 2 minutes. Add the black beans, bouillon, bay leaf and tomatoes, then add enough water to cover by an inch or two (about 4 cups).
Bring to a simmer and cook at least 30 minutes and up to 2 hours, adding more water if the soup is too thick; remove the bay leaf. Season with salt and pepper.
Serve with Cubano Sandwiches.
Split open and quarter 1 loaf French bread. Mix 2 tablespoons each mayonnaise and dijon mustard and spread on the bread. Sandwich with sliced Swiss cheese, deli-style ham, roast pork, pickles and more cheese. Butter the sandwiches, then cook in a cast-iron skillet over medium-high heat, pressing with a heavy skillet, 2 minutes. Flip, reduce the heat to medium low and cook, pressing, until golden, 1 more minute.