Prepare the jackfruit: Drain the canned jackfruit and lightly rinse under water, shaking off excess water. Use your fingers to remove any thick cores and pull the pieces apart so that it resembles shredded meat.
Heat a large skillet over medium-high heat and add the oil. Once hot, add the shredded jackfruit and cook for 4-5 minutes, stirring frequently, until the jackfruit begins to brown around the edges.
Make the buffalo sauce: Meanwhile, in a saucepan over medium heat, add the vegan butter (or coconut oil). Once melted, add the hot sauce, garlic powder, smoked paprika, pinch of kosher salt,, and maple syrup (or agave). Whisk together to combine and bring to a simmer.
Add the buffalo sauce to the jackfruit in the skillet, along with the 1/4 cup water. Stir to incorporate the sauce into the jackfruit, and reduce the heat to medium-low. Cook for 15 minutes, stirring occasionally, until the liquid has evaporated. Wipe out the skillet.
Assemble the grilled cheese: Drizzle the 8 slices of bread from both sides with just a tiny bit of olive oil. Top four slices with about 2 tablespoons of the Nut-Free Vegan Cheese Sauce (more if you like). Portion out ¼ of the jackfruit mixture onto each slice of bread, along with 1/4 of the spinach. Add another few tablespoons of the cheese sauce. Finally, top with the remaining slices of bread.
Heat the skillet over medium heat. Once the skillet is hot, cook each sandwich for 2 minutes, pressing down down on top with a spatula, or until golden brown on one side. Flip and cook for 1-2 more minutes, then remove from the heat.