For the seared tuna, season the tuna with salt and freshly ground black pepper, rub with olive oil and roll in the sesame seeds.
Heat a little olive oil in a frying pan, add the tuna and sear on all sides for 30 seconds. Remove from the heat and keep warm.
For the roasted sweet potato, heat the butter in a frying pan, add the sweet potato and fry for 8-10 minutes, turning frequently, or until golden-brown on all sides. Season well with salt and freshly ground black pepper and sprinkle over the toasted pine nuts.
For the pesto, place all the pesto ingredients into a mini blender and blend until smooth.
To serve, place the sweet potatoes onto a serving plate. Top with the seared tuna and spoon over the pesto.