duck

numQuads = 10000;
var verts = Vector3[numQuads * 4];
var uv = Vector2[numQuads * 4];
var tris = int[numQuads * 6];

for (var n=0; n<= numQuads; ++n)
{
    tris[n*6 + 0] = n*6 + 0;
    tris[n*6 + 1] = n*6 + 1;
    tris[n*6 + 2] = n*6 + 2;
    tris[n*6 + 3] = n*6 + 0;
    tris[n*6 + 4] = n*6 + 2;
    tris[n*6 + 5] = n*6 + 3;

    uv[n*6 + 0] = Vector2(0,0);
    uv[n*6 + 1] = Vector2(0,1);
    uv[n*6 + 2] = Vector2(1,1);
    uv[n*6 + 3] = Vector2(1,0);
}

mesh.vertices = verts;
mesh.uv = uv;
mesh.triangles = tris;