Small beaches and pretty place to view cliffs near Lisbon, Portugal?

You might consider a tour with Lisbon Riders. We spent the day touring Sintra & Cascais. Beautiful scenery, & knowledgeable Guide. It was a great introduction to Portugal. Our guide was Manuel. https://lisbonriders.com/

There are several very nice restaurants on the cliffs between downtown Cascais and Praia do Guincho.

Mar do Inferno is closest to town. Furnas do Guincho is one of my favorites. Casa da Guia (between the two I mentioned) has several not as fancy places but the views are spectacular.

You can also Google restaurants Guincho and find the ones closer to that area.

If you want to go toward Sintra, Praia Grande has several places but not on cliffs.