Preheat oven to 375F.

Mix flours, salt, and chopped thyme in a large bowl. Create a well in the middle, and pour in olive oil, ice water, and lemon juice. Mix liquids into the flour with a fork just until the liquid is absorbed and large clumps are created. Knead lightly 4-5 times, but no more, forming the dough into a ball.

Turn out dough onto a floured work surface. With a floured rolling pin, and working in quick, decisive movements, roll out the dough into a tart shape that is big enough to cover your tart form. Do not overwork the dough, just roll it out enough to ensure it'll cover your pan. When ready, gingerly lift the dough from the work surface and drape it over the tart shell. Cut off excess dough and discard (or roll it out, sprinkle with sea salt and herbs, and bake into a few crackers).

Meanwhile, in a small bowl mix vegan mayo with grainy mustard and 1 teaspoon of chopped thyme. Slice tomatoes into thick slices (about ½ an inch in thickness), and remove the seeds and excess juice from them (otherwise, your tart may get soggy - but you don't have to be too diligent about this, because you still want your tomatoes to keep some of their juiciness). Smear mayonnaise, mustard and thyme spread onto tart shell, and cover with tomatoes arranged in concentric, slightly overlapping circles.

Top with an additional teaspoon of chopped thyme, a pinch of salt, and some freshly ground black pepper.

Bake at 375F oven for 15 minutes, followed by another five minutes at 400F on the grill/broil setting (where the heat will crisp up your tomato a bit from the top). Serve hot, or even cold from the fridge - the tart keeps beautifully for a couple of days (just don't reheat in the microwave, please).