Heat oven to 375°F. Heat 2 tbsp. (4 tbsp. for 4 servings) olive oil in a large wide saucepan over medium. Add garlic, onion and red pepper flakes to taste. Cook for 3-4 minutes, stirring once or twice, until starting to brown.
While aromatics are cooking, slice sourdough bread into ¾ inch cubes. Wash basil and lemon. Pick and chop basil leaves. Zest and cut lemon in half. Rinse and drain black beans in a fine mesh sieve.
Add tomatoes, tomato paste, sugar, black beans, lemon zest, half of the bread pieces and half of the basil leaves to saucepan. Add spice blend and crumble in vegetable stock cube. Add 1 ½ cups (3 cups for 4 servings) water. Use a wooden spoon to break up and stir tomatoes into soup. Cover with a lid and cook for 15-17 minutes, until bread breaks down and soup reaches a porridge-like consistency.
Meanwhile, line a baking sheet with foil. Toss remaining bread on baking sheet with 1 tbsp. (2 tbsp. for 4 servings) olive oil, roasted garlic powder, and salt and pepper to taste. Bake for 10-12 minutes, turning once or twice, until golden and crispy. Remove from oven and set aside to cool.
Season + Finish Soup
Rinse and drain spinach in a sieve. Add spinach and balsamic reduction to soup. Add half of the lemon juice, salt and pepper to taste. Stir and cook for 1-2 minutes, or until spinach is bright green and tender.
Plate + Serve
Ladle soup into serving bowls. Top with remaining basil leaves and croutons. Squeeze remaining lemon juice on top if desired. Enjoy!