In this talk, our object of study is the Einstein-Vlasov system with a massless Vlasov matter field in topologically trivial spacetimes. Complementing various important works obtaining the stability of Minkowski spacetime as a solution to this system, we look at the large data regime, motivated in turn by the signature for decay rates of various Ricci coefficients, curvature and matter components, first introduced by X. An. Our work provides a semi-global existence result and a trapped surface formation result for the Einstein-Vlasov system in the absence of any symmetry and restriction on data size. Our proof is based on a double null gauge. Interestingly, we give a new way of obtaining estimates for the Vlasov matter, purely by commuting with various vector fields and without the need to use Jacobi fields. This is joint work with N. Athanasiou at Oxford.