Cook the pasta as per the packages directions. When ready, drain it and set it aside.
While the pasta cooks, start heating the oil in a large skillet over medium heat. When the oil is hot, add the garlic and shallot to the pan. Stir to coat, and simmer for about a minute.
Add the spinach, capers, and olives to the skillet, and sprinkle with a bit of sea salt. Simmer for about 5 minutes or until the spinach has wilted, stirring occasionally.
Transfer the tuna, as well as the olives and pimentos from the jar, to the skillet and stir it around, breaking the tuna fillets into large chunks.
Bring the cooked pasta to the skillet and drizzle a little more of the oil over the pasta; add the Dijon mustard. Squeeze a generous spritz of fresh lemon juice, and toss to coat. Crack some black pepper over the pasta and serve.