If you have buttermilk already, use that. Otherwise, combine one scant cup of milk with one tablespoon of freshly squeezed lemon juice. Let that sit for 5 to 10 minutes until it thickens and curdles a little bit.
Preheat the oven to 350°F. Grease your 8-inch round cake pans. This recipe can make either a 3 layer or 4 layer cake. Grease as many cake pans as you have/need. I made a four layer cake and I have two pans, so I baked the first two layers, popped them out and let the pans cool for about 10 minutes, then I re-greased the pans and baked the second two layers.
In the bowl of a stand mixer or a large mixing bowl, beat the melted coconut oil, yogurt, eggs, granulated sugar, brown sugar, vanilla, buttermilk (either store-bought or homemade), 1 tablespoon of lemon zest and ½ cup freshly squeezed lemon juice.
Add in 3¾ cups of flour, baking powder, baking soda and salt. Mix the it all together until the batter is just combined.
In a small bowl, toss the strawberries chunks with the remaining 1 tablespoon of flour. This helps coat the strawberries so they don't all sink to the bottom of the cake while it's baking. Fold the flour-coated strawberries and the strawberry jam into the cake batter.
Pour the batter into four separate bowls. To the first bowl, don't add any food coloring. To the second bowl, add a small squeeze of red gel food color. To the third bowl, add about three squeezes of the red coloring. And to the fourth bowl, add five squeezes to the batter. Stir them all and add more coloring as needed to achieve your desired levels of ombre.
Pour each bowl of batter into separate greased 8-inch round cake pans. Bake for about 30 - 35 minutes, until a toothpick comes out clean (aside from the jam) and the center of the cake isn't jiggly. Let the cakes cool for five minutes in the pans, then remove them and set them on a wire cooling rack to cool to room temperature.