Start by roasting your green peppers. You can do this either by placing them directly on a grill or under a broiler. Roast until the skin is charred and blistered, about 10-15 minutes, turning occasionally. Once done, place them in a bowl and cover with plastic wrap to steam. This will make peeling them easier. After about 10 minutes, peel off the skins, remove the seeds, and chop the peppers.
In a blender or food processor, combine the roasted peppers, minced garlic, lemon juice, ground cumin, ground coriander, sea salt, honey or maple syrup, cilantro, and pepitas. Add the olive oil and blend until smooth. Taste and adjust seasoning if necessary.
Lay out your slices of sourdough bread. Spread a generous amount of the pepper spread on one side of each slice. On half of the slices, layer a handful of fresh spinach and a good amount of grated Havarti cheese. Top with the remaining slices of bread, spread side down.
Heat a skillet or griddle over medium heat and add a splash of extra-virgin olive oil. Once hot, carefully place the sandwiches in the skillet. Grill for about 3-4 minutes on each side, or until the bread is golden brown and the cheese has melted. For an extra crispy texture, you can press down on the sandwiches gently with a spatula while they cook.
Once your sandwiches are grilled to perfection, remove them from the skillet. Allow them to cool slightly before slicing them in half. Serve warm, perhaps with a side of tomato soup or a simple salad for a complete meal.