In a small skillet over medium heat, add cumin, coriander and fennel seeds; toast until fragrant, about 2 minutes.
Let the seeds cool off for 15 minutes before transferring them into a spice grinder; grind to a fine powder.
Transfer spice mixture to a small bowl and add ras el hanout, paprika, cayenne pepper, cinnamon, harissa paste and garlic; mix until well blended.
In a mixing bowl, combine lamb and the spice mixture. Spread tomato paste on top and quickly mix with your hands.
Cover the meat tightly with plastic wrap and chill overnight.
The next day, form a small patty and cook it; taste and adjust the seasonings if needed. Proceed with sausage making or make patties.
Notes
Footnote: If you cannot find the harissa paste but only the spice blend, combine 1 1/2 tbsp. of it with 1 tsp. grapeseed oil and mix until it forms a paste.