Heat the oven to 425 F, and line a baking sheet with parchment paper.
Slice the plum tomatoes in half lengthwise, and then scoop out their seeds and jelly. Set the tomatoes cut-side up on the baking sheet. Drizzle them with 2 tablespoons extra virgin olive oil, and then sprinkle them with sea salt.
Roast the tomatoes for 30 minutes.
While you roast the tomatoes, prepare the pecan crumble. Toss the garlic, pecan pieces, marjoram and sage into a bowl with crushed red pepper and sea salt. Stir well.
Heat 1 tablespoon extra virgin olive oil in a skillet over medium heat. Stir in the pecan, garlic and herb mixture. Cook the pecans until they release a warm, toasty aroma - about 4 minutes. Stir them constantly to prevent scorching.
When the tomatoes are done, remove the baking sheet from the oven and top each tomato with a spoonful of toasted pecans. Turn down the oven to 375, and return the tomatoes to the oven. Continue baking a further 15 minutes. Serve warm, garnished with additional herbs if you like.