Trim the stalks and the root end of the fennel. Reserve some of the fennel fronds, but discard stalks and tough root. Cut the fennel bulb in half, and slice out the core. Discard core. Chop remaining fennel into ½-inch pieces.
Warm butter in a medium saucepan over medium heat. Add chopped fennel, scallion, garlic and jalapeño, and sauté until the fennel starts to soften (about 5 minutes).
Add coconut milk, and simmer for 2 minutes. Add water, rainbow chard leaves, and salt, and cook until the leaves are tender (about 5 minutes).
Transfer soup to a blender with a handful of baby spinach leaves, and blend until smooth. You can add a little water if the soup is too thick.
Season to taste with lemon juice (about ½ a lemon) and additional salt.
To serve, divide soup between 2 bowls (entree) or 4 bowls (appetizer), and top with Greek yogurt, toasted chopped almonds, toasted coconut flakes, sliced scallion greens, and pickled chard stems.
