Special equipment: Eight 6-ounce ramekins (preferably more wide than deep; it is easier to unmold the panna cotta if you fill the ramekins almost to the top)
For the chocolate-orange yogurt panna cotta: In a small bowl, sprinkle the gelatin over 1/2 cup of the milk. Let stand 1 minute, then stir and let stand until the gelatin softens, about 10 minutes more.
In a medium saucepan, whisk together the remaining 1 1/2 cups milk, the sugar, semisweet chocolate and cocoa over medium heat until just beginning to simmer, about 3 minutes. Add the gelatin mixture and whisk gently until it dissolves, 2 to 3 minutes. Remove from the heat and let cool completely, about 10 minutes.
Spray the ramekins with the cooking spray. In a large bowl, whisk the yogurt with the orange zest and vanilla extract until smooth. Pour the cooled chocolate mixture through a fine strainer into the yogurt and whisk until smooth. Divide the chocolate yogurt mixture among the prepared ramekins. Cover and chill overnight.
For the chocolate-coconut granola: Position a baking rack in the middle of the oven and preheat to 275 degrees F. Brush a baking sheet with 1 tablespoon of the coconut oil and set aside. Combine the oats, almonds and coconut chips in a large bowl and set aside.
Heat the remaining 1/4 cup coconut oil in a small saucepan over medium heat. Whisk in the cocoa powder, honey, sugar and salt and bring to a simmer. Cook, whisking constantly, until smooth and the sugar is completely melted; stir in the coconut and vanilla extracts.
Pour the warm cocoa mixture over the oat mixture and fold in with a rubber spatula until the oat mixture is completely coated. Transfer the mixture to the prepared baking sheet and press into an even layer. Bake for 50 minutes. Turn off the oven and let sit in the warm oven for 30 minutes longer. Remove to a cooling rack and cool to room temperature. Break into bite-sized pieces, and toss with the bittersweet and white chocolate chips.
You can serve the panna cotta in the ramekins, or unmold them onto individual serving plates. To unmold, run a small metal spatula between the set panna cotta and sides of the ramekins to loosen. In a bowl of hot water, immerse the ramekins one at a time to just below the rim until the edges of the dessert soften, 20 to 30 seconds. Remove and dry the bottom of the ramekin. Invert a small plate over the top of each ramekin and give a firm shake to release the panna cotta, easing it out gently with the spatula if needed.
Top each panna cotta with the chocolate-coconut granola and sliced orange segments, if using.