In a small pot of boiling water, blanch the asparagus briefly (this will set its color). Remove from heat.
Using a sharp paring knife, make three incisions in the end of the tuna, lengthwise. Insert the three blanched asparagus spears. In a small bowl, beat the eggs. Dip the tuna in the eggs to coat, then coat with the mixture of flour, bread crumbs and salt.
In a small sauté pan, melt the butter, then add the spinach and sauté until wilted. Set aside.
In a sauté pan over medium heat, sear the tuna filet to desired temperature. Remove from heat, and slice the tuna in 1 inch thick pieces. Serve with the sautéed spinach, and shave foie gras over the top.