Preheat oven to 350°F and grease a 13 x 9 inch baking dish with vegetable spray.
Combine strawberry cake mix, guava nectar, eggs, and melted coconut oil in a mixer. Blend on low for 30 seconds, scrape sides, then beat on medium-high for 2 minutes.
Pour batter into prepared pan and bake for 24 to 26 minutes, or until a toothpick inserted comes out clean.
Cool cake completely on a wire rack.
Beat cream cheese until fluffy, then add sugar and vanilla extract and mix. Gently fold in thawed Cool Whip and refrigerate until needed.
Spread cream cheese mixture evenly over cooled cake and chill to set.
For guava gel, bring 2 1/2 cups guava nectar and sugar to a low boil in a saucepan.
Mix cornstarch with water to form a slurry, then whisk into the boiling guava mixture.
Boil for one minute until thickened, then cool the gel in the refrigerator.
Spread cooled guava gel evenly over the cream cheese layer on the cake.
Refrigerate until serving and garnish with sweetened coconut flakes if desired.