Coat a (10 -12 cup capacity) bundt pan with a little bit of vegan butter or vegetable cooking spray. Set aside.
Place coconut milk in a medium sauce pot, and bring to a simmer.
While the milk is heating up, combine the oat milk, cornstarch, sugar, chickpea flour, and vanilla in the blender and process until smooth. Pour this mixture into the pot with the coconut milk. Add food coloring if using, mix to combine.
Bring mixture to a simmer for 5 minutes, then remove from the heat, and pour into the bundt pan. Give it a little shake to evenly distribute the flan mixture in the bottom the pan. Set aside.
Preheat oven to 350°F
Sift the flour, cocoa powder, sugar, baking soda, and salt into a large bowl and mix to combine. Make a well in the center of your bowl and add the vanilla, oil, vinegar, and water. Whisk until smooth.
Pour cake batter on top of the flan mixture already in the bundt pan.
Place a sheet tray with water in the center rack of the oven (this will function as our water bath) and place bundt pan in the center of the sheet tray. Bake for 45-50 minutes or until a toothpick inserted into the cake comes out clean. (Be careful not to insert the toothpick all the way to the bottom of the bundt pan, we just want to test the cake, not the flan).
Remove cake from the oven and let cool. Place in fridge for at least four hours or until it is completely cool. Pass a butter knife around the edges of the bundt pan only at the cake level. Place the flan part of the cake in a warm water bath for 2 minutes, so the flan unsticks from the pan. Flip the bundt pan over onto a plate and give the bundt pan a shake. The cake should slide out. If it doesn't slide out, place the cake back in the water bath and try again.
Garnish with vegan cajeta and chopped pecans.
I used my recipe for vegan cajeta to top the cake, but you could also top it with a vegan caramel. You can use your favorite chopped nuts. Make sure to lightly coat your mold in vegan butter or a cooking spray so the cake is easy to unmold. If you have trouble unmolding, place the mold in a warm water bath, at the level of the flan, for a couple of minutes then try unmolding it. If the cake doesn't unmold:Place the flan part of the cake in a warm water bath for 2 minutes, so the flan unsticks from the pan. Flip the bundt pan over onto a plate and give the bundt pan a shake. The cake should slide out. If it doesn't slide out, place the cake back in the water bath and try again.