Place the ground cumin and coriander into a bowl and mix to combine, then place the tuna into the spices. Roll to coat and leave to marinate for 20 minutes.
Heat an ovenproof frying pan until hot then add the tuna. Cook on each side for 15-20 seconds, just to lightly brown the tuna. Transfer to the oven to roast for 3-4 minutes, until just cooked but still pink in the centre, or until cooked to your liking.
Meanwhile, for the dressing, place the garlic, anchovies and egg yolk into a pestle and mortar and pound to a paste.
Add the lemon juice and the olive oil, and mix well.
Add the mustard and season, to taste, with salt and freshly ground black pepper.
To assemble the salad - place the beans, potatoes, olives and eggs into a bowl, add the dressing and mix well. Transfer onto a serving plate, cut the tuna in half and place on top.
Rub the toasted baguette slices with the garlic clove, then top with the tomatoes. Place the tomato toasts around the edge of the salad and serve.