Start to cook the bacon so that it becomes crisp. Meanwhile combine the mayonnaise with lemon juice, garlic, turmeric and ground cumin and season to taste with salt and pepper. Pan grill the bread, just until dried out or toasted; pan grill the tuna, only 3 minutes a side, or until rare.
Remove bacon to paper towels to drain.
To assemble, spread each slice of bread with mayonnaise, on one side only. Slice the tuna into thin diagonal pieces. Set some arugula on bottom of bread, then top with bacon, peppers and tuna and bread, mayonnaise side down; repeat and finish with third slice of bread; repeat for the other sandwich.