Preheat oven to 425F. Line a baking sheet with parchment paper or silicone baking mat.
Combine the water and ground flax seeds in a blender and blend at high speed for 30 seconds. Pour into a wide, shallow bowl and allow to sit for a few minutes to thicken slightly.
In another wide bowl or plate, combine remaining ingredients (except tomatoes). Cut tomatoes into slices about 1/4 to 1/2-inch thick. Submerge a tomato slice in the flax-water, allow excess to drip off, and place slice into cornmeal mixture. Press lightly to make sure that bottom of slice is covered with cornmeal and turn to coat other side. Place on prepared baking sheet.
When all tomato slices are coated, bake for 15 minutes, or until bottoms are golden brown. Turn and bake another 15 minutes to brown other side. Remove from oven and serve immediately.