In a saucepan, heat the oil over medium heat.
Cook the onions slowly until they are softened and golden brown on the edges (about 5 minutes).
Add the ginger and garlic. Cook for 5 minutes more.

Add the curry paste, cinnamon, coriander, and cumin, then let it simmer until the mixture starts to smell fragrant (about 1 minute).
Add the chicken and cook for about 10 minutes or until the chicken pieces are coated with spices and lightly browned.
Season to taste and transfer the chicken to a bowl.

Add the coconut milk and tomatoes, making sure to scrape the bottom of the pan to remove any stuck pieces. Bring to a boil.
Reduce the heat and let it simmer for 10 minutes or until the sauce has thickened.

Return the chicken pieces to the sauce and simmer, uncovered, for 2 or 3 minutes or until the chicken is almost fully cooked.
Remove from heat, then stir in the lemon juice, spinach, and raisins.
Check the seasoning and add salt or lemon juice as needed.