For the crust, stir together the flour, sugar, salt, garlic powder, oregano, thyme, and black pepper in a bowl until combined. Grate the frozen butter over the bowl using the large hole setting of a grater, pausing every 10 seconds to stir the butter shards into the flour so they don't all stick to each other. Add the ice water and stir to combine, then knead with your hands until the dough comes together. If it crumbles apart, add another tablespoon or two of water. If it's too sticky, add another tablespoon or two of flour. Roll out the dough on a large cutting board so that it's 1/4 inch thick. Cover and refrigerate.
For the caramelized tomato + chevre filling, melt the butter in an 8 to 10-inch skillet skillet over medium low heat. Add the onion, garlic, and 1/2 teaspoon sugar and stir to combine. Continue cooking until the onions soften and turn lightly gold around the edges, about 20 to 30 minutes, stirring every 5 minutes.
Preheat the oven to 425 degrees Fahrenheit. Scrape the contents of the pan into a heat-safe bowl and set it aside, placing the pan back over the heat. Add the remaining sugar and water to pan and bring to a boil over high heat. Reduce heat to medium and allow to boil, swirling the pan gently to mix, until the sugar caramelizes, becomes very fragrant, and looks amber when scooped with a steel spoon, about 5 to 10 minutes.
Reduce the heat to medium low and add the cherry tomatoes, salt, thyme, and pepper to the pan. Cook for 5 minutes to help soften the tomatoes, then evenly distribute the caramelized onion mixture over the tomatoes and sprinkle with the chevre. Remove from heat and place the crust over the top of the skillet, trimming off the excess and using a blunt butter knife to tuck the edges of the crust into the pan.
Use a sharp knife to poke 5 hole in the top of the crust. Place the pan in the oven and bake until the crust is lightly golden on top, about 35 minutes. Remove from the oven and place a heat-proof plate on top of the pan. Invert the pan and lift it off of the plate, so that the tomato tarte tatin is now resting tomato-side up on the plate. Allow to cool for 10 minutes before slicing and serving.