Heat a little oil in a medium saucepan on a medium high heat. Add beef and cook, stirring for a few minutes - until the beef is no longer pink and starting to brown.
Add lentils, tomato passata / puree, spice / curry powder, a big pinch salt and 1.5 cups water. Cover and bring to a rapid simmer.
Simmer, covered, on a medium heat for about 10 minutes. Stirring once or twice. If the pot is drying out add an extra 1/2 cup water. While the lentils are cooking dice or crumble the feta.
Continue to simmer and stir until the lentils are cooked to your liking. I like them soft but not falling apart and still with some bite like al dente pasta.
When the lentils are cooked, taste and season with more salt and more spice if needed.
Divide baby spinach between two bowls. Top with lentils and finish with feta.