Trim the bases off the fennel bulbs, along with any woody tops. Save any fronds for later in the recipe. Halve and thinly slice the fennel bulbs. Peel the onions and thinly slice them. Peel and crush or finely chop the garlic. Pick the rosemary leaves off their stalks and finely chop the leaves.
Pour 1 tbsp oil into a large pan and bring to a medium heat. Slide in the onions, fennel, garlic and rosemary. Sprinkle in 2 tsp smoked paprika, 2 tsp ground cumin and a generous pinch of salt and pepper. Fry for 12-15 mins, stirring often, till the veg are softened and slightly browned.
While the veg cook, peel the potatoes. Cut them into 1-2cm-thick chunks. Fill and boil your kettle.
Slide the potatoes into the pan. Tip in the tin of cherry tomatoes. Crumble in the stock cube and pour in 1 ltr boiling water. Pop a lid on the pan. Return the stew to the boil, then reduce the heat to a simmer and cook for 30 mins, till the potatoes are tender.
When the stew is nearly ready, stir in the spinach leaves. Grate in the lemon zest. Squeeze in half of the lemon juice. Taste the stew and add more salt and pepper or lemon juice if needed.
Ladle the stew into deep bowls and drizzle a little olive oil over the top of each dish. Scatter over any reserved fennel fronds and serve.