Put the pineapple, kale, frozen grapes, lemon juice, ginger and flaxseed into a blender. Blend on high until very smooth, turning off the blender and pushing down on the ingredients with a spatula or wooden spoon as needed to help the blending process. Add 1 to 2 tablespoons of water if needed to adjust consistency. Pour into a glass and garnish with a pineapple wedge.