Chop chocolate into small pieces and melt completely in a double boiler or microwave.
In a large bowl, combine chocolate, lamb, mint, and spices. Mix thoroughly.
Divide the seasoned ground lamb into four patties.
Heat canola oil in a non-stick skillet over medium-high heat.
Add patties to the oil and cook thoroughly, approximately 5 minutes per side.
Lightly toast hamburger buns.
Place each patty onto the bottom half of a bun. Spread homemade ketchup (below) on top of the patty, to taste. Garnish with arugula and cover with the top of the bun.